1. Field of the Invention
This invention relates to an impulse heat jointer for wrapping tapes of wire cables.
2. Description of the Prior Art
For the outer sheath of the communication cables, aluminum or steel tapes of flat and corrugated type have been generally used but recently, there is an increasing demand for the cables sheathed with laminated tapes, that is, metal coated on either or both sides thereof with plastic films. These laminated tapes are wrapped around the cable cores longitudinally or helically during the plastic sheath process for the cables. Since the plastic sheath process should naturally be carried out continuously for a considerable length of time, in view of cable manufacturing costs, working efficiency and uniform quality in the resulting product, the tapes for longitudinal wrapping should accordingly be supplied continuously and hence, the tape ends should be rapidly joined. Moreover, requirements for the mechanical strength in the joined portions of the tapes in particular the tensile strength and peel off strength of the joined portions and the peel off strength between the joined portions and the outer sheath have become stringent. In addition, achieving good electrical conductivity in those portions also becomes necessary.
In order to satisfy these diverse requirements, various joining methods have been developed and reported in the literature. These include, for example, a mechanical method in which the joint is effectuated by embossing the surfaces of two tapes to be joined or, alternatively, a method of applying continuous seam welds to the tapes, traversely.
A prior art system for applying the outer sheath to the cables is shown in FIG. 1 and FIG. 2, wherein reference numeral 1 denotes a tape supply source constructed in a dual system for the convenience of continuous tape supply. There is also shown a tape jointer 2, a tape accumulator 3 for storing sufficient amount of tape for supplying over the time required for the joint, an apparatus 4 for longitudinally applying the tape on the cable core, an extruder 5 for applying plastic coating on the cable and a cooling water trough 6 for use with cooling after the plastic coating.
The cross section of a joined portion of the tape according to the conventional mechanical joining method described above in shown in FIG. 3, wherein there are shown laminated tapes 10a and 10b, metal surfaces 11a and 11b thereof, the surfaces of the plastic films 12a and 12b laminated to said metal tapes, an active press block 13 embossed at the bottom thereof, a passive press block 14 also embossed at the surface thereof.
In this joining method, tapes to be joined are put between the active press block 13 and the passive press block 14 by lowering the former to the latter while applying an appropriate pressure thereon, and are then embossed at the adjacent surfaces and then joined mechanically.
This method is, however, unsatisfactory in that the peel off strength in the joined portions of the tape is poor and the electrical conduction between the tapes in insufficient due to the plastic layer left between two tapes that are joined.
FIG. 4 shows the joined portion of tapes made through the seam welding according to another prior art joining method, wherein there is shown laminated tapes 10a and 10b, surfaces of the metal sides 11a and 11b of the laminated tapes and surfaces of the plastic films 12a and 12b laminated to the metal sides. The seam portion is located at position B.
The method just described above is unsatisfactory in that the laminated plastic material must be removed from the upper tape at the joint portion prior to the joining and as can be seen from the drawing, the edges (Positions A in FIG. 4) of the joined tapes tend to turn up. Also, the tapes in the vicinity of the welded portions are reduced in strength while the seam welded portion per se possess considerable strength. This discontinuity in material quality along the tape is unacceptable.